The evaporator temperature sensor can fail, causing the AC compressor not to cycle. If the AC compressor does not turn on, the AC system will not blow cold air. If the compressor is stuck on, the air will be very cold at first, before warming up.Google+
Car Problem Reports
Mercedes-Benz S500 Evaporator Temperature Sensor Failure
Mercedes-Benz S500 Problem
Average Mileage: 136,206 mi (45,000 mi - 238,000 mi)
Mine quit at the above mileage some years ago. Abourt $300 parts and labor at the dealer. Failure causes A/C to freeze up and blocks airflow. After a few days of this, the A/C shut itself off to prevent damage...the ECON button stays lit up to tell you something is wrong.
Visitor, 2000 Mercedes-Benz S500, 238,000 mi
Fan stoped working got a new blower unit now it's working but my a/c is not .